‘Foreign Objects’ (FOs) refers to any unwanted object in beverage product. Detection of FOs in beverages plays an important role in security control and quality assurance of food products. When beverages are manufactured or packaged small foreign objects might end up in the product. Fragments of glass and metal scarf may be found in glass jars or cans. It is naturally desirable for beverage production that all FOs are found and removed before they reach the consumers.
Mechanical separation techniques have been used for many years for finding foreign objects in powdered and flowing products on the basis of size and weight. See e.g. A. J. Campbell, “Identification of Foreign Body Hazards and the Means for their Detection and Control,” (Technical Bulletin No. 88, UK: Campden Food & Drink Research Association. 1992). This method is appropriate only before the beverage is packaged in bottles or containers. Optical techniques can be used for after container filling inspection, as described by T. Gomm and S. E. Price in U.S. Pat. No. 4,136,930 entitled “Method and apparatus for detecting foreign particles in full beverage containers” issued in 1979, and by P. Weathers in U.S. Pat. No. 2,427,319 entitled “Beverage inspection machine” issued in 1947, but they are limited to clear transparency beverage bottles. X-rays and magnetic resonance imaging (MRI) could be another options but they are expensive, safety uncertain and complicated methods. See e.g. B. Zhao, O. Basir and G. Mittal, “Prototype of Foreign Body Detector for Beverage Containers by Ultrasonic Technique,” submitted to Food research international in 2002, and B. Zhao, O. Basir and G. Mittal, “Foreign Body Detection in Foods by Ultrasound Pulse/echo Method,” submitted to International Journal of Food Science & Technology in 2001.
Low intensity ultrasonic techniques can be used in beverage inspection because of their large applicability, reliability, safety and low cost. Nevertheless, there are only a limited number of publications related to packaged food inspections. For example, “Container inspecting apparatus,” described by K. Tadahisa, K. Kunihiko, M. Yasuo and N. Masaji in E.P. Pat. No. 0821230 issued in 1998, which uses ultrasonic vibration to agitate effervescence of beverage from the bottom of the container to inspect the sealing performance.
The second publication is “Preliminary studies of a novel air—coupled ultrasonic inspection system for food containers” presented by T. H. Gan., D. A. Hutchines, and D. R. Billson, Journal of Food Engineering, vol. 53, pp 315–323 (2002) in which FO suspended in low density material container (soft drink bottle) was tested using air coupled transducers in thru-transmission mode.
Air coupled ultrasonic techniques have two drawbacks. One is that its application is limited to low density material due to the reflection of most of the transmitted energy because of acoustic impedance mismatch. The second is that this technique works in mode of separate transmitter and receiver. This mode is employed for either thru-transmission or surface wave detection. Thru-transmission is not a good mode for inspecting FOs sediment at the bottle bottom because the ultrasound signal can not transmit from the transmitter to receiver when they are separately placed under the bottom and above the top of the bottle being inspected. This is due to the bottle neck which shields the ultrasonic longitudinal transmission from bottom to cover. Surface wave technique detects flaws in a material by examining the time of flight of a pulse with respect to that of a back wall echo (inner surface of the container wall). This method is not suitable for detecting FOs inside a container since the presence of FOs does not change the time of flight from the inner surface of the bottle wall.
Water coupling can be used in high density container materials inspection. See. e.g. E. Haeggestrom, and M. Luukkala, “Ultrasound Detection and Identification of Foreign Bodies in Food Products”, Food Control, vol. 12, p37 (2001), and M. Hiroshi, I. Sigeki, K. Tsukio, and N. Masanori in K. R Pat. NO. 9,005,245, entitled “Inspection method and apparatus for wrapped contents by ultrasonic,” which is issued in 1990. however, in both of the publications the water tank immersion mode are used, which is not suitable for bottled beverage production on-line inspection because of its low inspection speed. See e.g. Y. Jiang, B. Zhao, O. Basir and G. Mittal, “LabView Implementation of an Ultrasound System for Foreign Body Detection in Food Products,” submitted to Computers and Electronics in Agriculture in 2002.
In summary of the above-published ultrasonic techniques for food inspection, a fatal drawback is that they use point-detection (using one transducer or one pair of transducers). Only one small point of food container can be inspected each time by one transducer or transducer pair, which cannot catch up with the high speed food production. Their methods are therefore not suitable for on-line FOs inspection
Product rating is another point for manufactures to optimize their pricing and sale strategy. Viscosity is one of indices for product quality rating which can indicate the juice concentration, mouth feel, the ingredient functionality, and shelf life. Conventional liquid viscosity measurement is conducted by Couette, plate-and-cone rotational, and parallel plate rheometers based on Poiseuille or Couette flow or oscillating flow. A drawback of these conventional methods is that they are normally conducted off-line. This makes it difficult to monitor product quality in real-time. Especially, this off-line inspection is an open-bottle percentage sampling method, i.e., one judges the quality of a bench of production based on the examination of one or two samples. The beverage quality in each individual closed bottle is different from each other but in fact is not known. Therefore, the quality of an individual bottle may be over-evaluated by the bench evaluation, which damages the reputation of the producer when it reaches consumers. In the opposite case, the producer loses money if the quality is under-evaluated by the bench evaluation.
Being rapid, non-destructive and non-invasive, ultrasonic technique is a promising approach for viscosity on-line measurement in food processing industry. Using ultrasonic technique the viscosity measurement can be approached by establishing a correlation between the viscosity of beverages and other measured physical properties of the ultrasound signal. R. Saggin, and J. N. Couplant described an ultrasonic reflectance coefficient method in “Ultrasonic characterization of oil viscosity and solids content” (2000 IFT Annual Meeting, Dallas, Tex. Jun. 11–14, 2000; 30D-11). An advantage of this method is that it only requires the reflection signal at one interface. However, this technique employs both amplitude and phase information at several frequencies to determined the viscosity. This makes the viscosity computation process relatively complicated. Furthermore, computing phase response in the spectrum is less accurate than that of computing amplitude response. M. J. McCarthy, R. L. Powell, J. A. Fort, D. M. Pfund, and D. M. Sheen presented ultrasonic Doppler velocimetry for food viscosity measurement, “Development of ultrasonic Doppler velocimetry for viscosity measurements” (2000 IFT Annual Meeting. Dallas, Tex. Jun. 11–14, 2000 nr 49-6). They used ultrasonic Doppler Velocimetry to determine the velocity profile in a tube. This technique needs not only an accurate velocity measurement, but also an accurate spatial measurement and subsequent data fitting for the profile. See e.g. B. Zhao, O. Basir and G. Mittal, “Correlation Analysis between Beverage Viscosity and Sound Velocity,” submitted to International Journal of Food Properties in 2002.
Velocity measurement by pulse/echo method is the simplest, widely used, and probably the most accurate in ultrasonic techniques. Using velocity of sound as a measure of beverage viscosity requires a governing law to predict how the viscosity is correlated with the ultrasound velocity. However, there is no direct or explicit correlation between the viscosity and the velocity of sound. Furthermore, using time-of-flight measurement to correlate the fluid viscosity is normally performed in a conduit of volume flow, as described by M. Guitis in D.E. Pat. No. 19940192, entitled “Device for determination of fluid parameters and fluid composition control based on on-line measurement of such fluid parameters using twin ultrasonic transducer and reflector arrays for accurate measurement of fluid parameters,” which is issued in 2001. The viscosity obtained by this way is not the viscosity in each individual bottle. The time-of-flight in that patent is measured in such a way that the transmitter and receiver or reflector are well aligned and their distance is fixed. These conditions, good alignment and fixed distance, are not available for a beverage bottle: curvature of bottle surface demands a strict alignment, perception of as small as 1% variation of sound speed in beverages needs to on-line measure the real bottle diameter and wall thickness of each sample instead of using the nominal thickness.